1. Field of the Invention
This invention relates to a heat developable photosensitive material. More specifically, it relates to a heat developable photosensitive material having excellent sensitivity and storage stability, which comprises a nitrogen-containing organic base whose conjugate acid has a pKa of from 0.5 to 10.0.
2. Description of the Prior Art
Conventional wet processing photosensitive materials using a silver halide emulsion are excellent in their sensitivity, gradation and image quality, but they need complicated time consuming processes using various treating chemicals in obtaining stable images. Further, the chemicals used give rise to a pollution problem. Accordingly, there have been proposed many photosensitive materials capable of forming images thereon easily only by dry processing in a short period of time without using treating chemicals. Such heat developable photosensitive materials use an organic silver salt oxidizing agent as its main component and may be classified into two groups. One is a pre-activation type heat developable photosensitive material on which images can be formed by the imagewise exposure and then the heat development, and the other is a post-activation type heat developable photosensitive material which is non-photosensitive under normal light conditions and can be rendered photosensitive by the preliminary heating prior to the imagewise exposure. For example, the former is described in U.S. Pat. Nos. 3,152,904 and 3,457,075, and the latter is described in U.S. Pat. Nos. 3,802,888 and 3,764,329.
However, the sensitivities of these heat developable photosensitive materials thus proposed are remarkably lower than those of the conventional photosensitive materials containing a silver halide emulsion, and thus utilization of these heat developable photosensitive materials for general purposes are still limited.